Yes and no.
I haven't noticed a timer for them going away but I have noticed loading bugs.
If you quickload to fast sometimes the engine forgets to repopulate a corpse or two, or just their guns. Like last night I was in the Capitol building, killed a mutie who was on some scaffolding with a minigun. he dropped his gun by his body and i quicksaved. I them was ambushed by 4 or 5 Talons, died loaded his body was still there, but i reloaded quickly out of habit not liking to load from dieing, and no body just the gun. After dieing one more time and reloading again no gun or body existed just blood splatter.